1. Field of the Invention
The present invention is directed generally to an apparatus and method of monitoring a subject's eyes and, more particularly, to an apparatus and method using light of two different wavelengths to monitor a subject's eyes.
2. Description of the Background
It is known in the art to monitor a subject's eyes, such as to measure "perclos". Perclos, generally, is a measure of the proportion of time that a subject's eyes are closed, either completely or beyond a predetermined point. For example, perclos may be the measure of the proportion of time that a subject's eyes are between 80% and 100% closed. Often, the measurement of perclos must be done manually, such as by videotaping the subject, reviewing the tape, and measuring the subject's perclos. Such a method, of course, is not practical for many applications.
Another method of determining perclos involves the use of an image sensor, such as a video camera, and image processing software to monitor the subject, determine the location of the subject's eyes, and determine the subject's perclos. That method, however, is time consuming and often cannot be performed in real time, thereby prohibiting it from being used to determine the drowsiness of a driver of a motor vehicle. One attempt to overcome that problem is to monitor only a portion of the subject's face, the portion containing the subject's eyes, thereby reducing the amount of processing required to determine perclos. That approach, however, creates another problem. The problem arises because the subject's eyes must be tracked as they move to monitor the road and as the subject's head and body move. Often, however, the subject moves quickly and the subject's eyes cannot be tracked. As a result, the prior art devices must search for the subject's eyes and, until the subject's eyes are located, the prior art devices cannot determine perclos.
Another deficiency with the prior art, regardless of whether the subject's entire face or only the subject's eyes are monitored, is that the prior art devices have difficulty finding and monitoring the subject's eyes. For example, the prior art devices often cannot distinguish between the subject's eyes and other sources of light and reflected light, such as is caused by dashboard lights, lights from other vehicles, and street lights. Those problems are exaggerated when the subject is wearing glasses.
Therefore, there is a need for a device and method for monitoring the eyes of a subject, such as can be used to determine perclos. The need exists for such a device and method that can operate in real time, can monitor the entire face of the subject, and is insensitive to other sources of light.